Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved DISTRIBUTED SYSTEMS Principles and Paradigms Second Edition ANDREW S. TANENBAUM MAARTEN VAN STEEN Chapter 12 Distributed Web-Based Systems

12.1 Architecture (5) traditional web-based systems, web services 12.2 Processes (3) clients, the Apache web server, web server clusters 12.3 Communication (4 + x) hypertext transfer protocol, simple object access protocol, (DASH) 12.4 Naming (1) 12.5 Synchronization (0.5) 12.6 Consistency and replication (6) web proxy caching, replication for web hosting systems, replication of web applications 12.7 Fault tolerance (0.5) 12.8 Security (0.5) Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved

1 Architecture Naming 2 Communication + DASH 3 Consistency and replication Syn. 4 Processes Fault tole Sec. Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved

Traditional Web-Based Systems Figure The overall organization of a traditional Web site.

Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved Web Documents Figure Six top-level MIME types and some common subtypes.

Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved Multitiered Architectures Figure The principle of using server-side CGI programs.

Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved Web Services Fundamentals Figure The principle of a Web service.

Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved Processes – Clients (1) Figure The logical components of a Web browser.

Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved Processes – Clients (2) Figure Using a Web proxy when the browser does not speak FTP.

Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved The Apache Web Server Figure The general organization of the Apache Web server.

Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved Web Server Clusters (1) Figure The principle of using a server cluster in combination with a front end to implement a Web service.

Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved Web Server Clusters (2) Figure A scalable content-aware cluster of Web servers.

Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved HTTP Connections (1) Figure (a) Using nonpersistent connections.

Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved HTTP Connections (2) Figure (b) Using persistent connections.

Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved HTTP Methods Figure Operations supported by HTTP.

Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved HTTP Messages (1) Figure (a) HTTP request message.

Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved HTTP Messages (2) Figure (b) HTTP response message.

Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved HTTP Messages (3) Figure Some HTTP message headers.

Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved HTTP Messages (4) Figure Some HTTP message headers.

Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved Simple Object Access Protocol Figure An example of an XML-based SOAP message.

Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved Naming (1) Figure Often-used structures for URLs. (a) Using only a DNS name. (b) Combining a DNS name with a port number. (c) Combining an IP address with a port number.

Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved Naming (2) Figure Examples of URIs.

Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved Web Proxy Caching Figure The principle of cooperative caching.

Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved Replication for Web Hosting Systems Figure The general organization of a CDN as a feedback- control system (adapted from Sivasubramanian et al., 2004b).

Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved Adaptation Triggering Figure One normal and three different access patterns reflecting flashcrowd behavior (adapted from Baryshnikov et al., 2005).

Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved Adjustment Measures Figure The principal working of the Akamai CDN.

Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved Replication of Web Applications Figure Alternatives for caching and replication with Web applications.

Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved Security (1) Figure The position of TLS in the Internet protocol stack.

Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved Security (2) Figure TLS with mutual authentication.